Switched mode power supply systems are used for a wide range of applications from simple AC to DC converters used for power consumer products, such as computers and audio appliances, to high power converter systems used to provide power to electric cars and rack mounted premises equipment used in large computer and communication network facilities. In higher power switched mode power supplies, such as those used to power communication equipment, there is often a requirement that the input and output power ports are galvanically isolated in order to facilitate operation across more than one power supply domain and to prevent injury due to high currents in ground loops.
As many switched mode power supplies provide a regulated output, a voltage and/or current feedback path is often used. In order to maintain galvanic isolation, however, this feedback path is also galvanically isolated via isolation transformers and optocouplers. For example, in some systems, the output voltage of the switched mode power supply is converted to a light intensity in the output power domain using a light emitting diode (LED). This light intensity is received in the input power domain via a photodiode, the output of which is used to derive an error signal for the voltage control loop. In very low cost, high volume consumer applications, however, the existence of optocouplers and isolation transformers in the feedback path add extra cost and consume board space. Even in systems that do not require galvanic isolation, components needed to facilitate voltage and/or current feedback may also add cost and/or board space to the system.